I've been struggling with problems with my 12.5 b&s vertical shaft motor. It ran low on oil a while back, it never seized... but it did stop from the friction. I simply took the head off & lubed the cylinder wall with oil & worked the piston by hand via the flywheel. I put the head back on & then it started right up &I finished my lawn.

The next time I stated the mower,the connecting rod broke. After re-assembly & start up, the motor would not run right, so I took it apart again & changed the rings. Then after re-assembly the connecting link broke. After replacing th connecting link, I started it up & the (new) link immediately broke again!

Has anyone had these issues? Or... know what I might be doing wrong?
I am at a loss with this motor.

I have had it apart 3 times & am about ready to junk it!
Hope someone can give me some pointers... Thanks!

Rob

Do you have a repair manual? I'd buy one for that particular engine... has all the specs you need to go by.. you could (from what it sounds like) left the conrod endcap too loose or tight.

Thanks Briggs dude...

I actually found out what it was last night. I had not pressed the pin that holds one end of the connecting link into the crank case far enough when I replaced it. So, the pin came out of the hole & the connecting link was flapping on the inner wall of the crank case whenI started it. The link did not break, but it did end up cracking some so I am going to replace it again. Fortunately, I shut the egine down right after the noise started. Sorry to have posted this as I answered my own question! LOL. I should have dis-assembled the engine first. Thanks again!

Btw, it didn't hit the engine did it? You do run the risk of stress cracks in the block.

No, it just slapped against the inner wall of the crank case. Luckily, as the link is pivoted off the other pin in the counterweight. There seems to be no visible damage to the crank case though.

I can say one thing abouit this whole experience, I've gotten fairly proficient timewise on getting the motor off the mower & dis-assembeled. I can get the motor off the mover & all apart on the bench in about 45 min.
The fisrt time It took me about 3 hours. Of course, my haste for getting it back together the last time could have been the cause of the problem this time around! LOL

Lol, Just did a swap on mine... took all of 2 hours, replace a 12hp single with a 18hp apposed.. had to swap the wiring and all... biggest problem was the stuck bolts on the 18 horse.. and the loads of rusty bolts I broke half of getting it off.

Well, again I continuue to have problems! I replaced the connecting link & tapped in the pin that connects it to the crank case & re-assembled it.
Started right up & ran fine. When I went to engage the blades it let go again.

I think the hole the pin goes in (in the cank case) is worn & it does not have a good tight press fit like it did originally. Hence, the pin falls out when a load is put on it & the connecting link ends up flapping up and down when the crank turns. The crank case is aluminum & the pin is hardened steel. (makes sense for the hole to be worn) I've thought about making a pin that is a little oversized so it fits the hole tighter.
I have not dis-assembld it yet, but am about sick & tired of this motor!
I am looking into a used 12 hp that runs & is on a mower without a deck for $75

I am beginning to wish I did that from the start!

Makes me mad, every time I get the darn thing back together... something else gives me problems. Well, I've learned quite a bit with the whole experience though. Not all bad I guess!

Thanks !

You mean the pin that connects it to the piston? (wrist pin) connects the rod to the piston.. the only other thing that connects the rod is the two bolts on the end cap (and it should be torqued to spec (forget exactly for that engine) and a NEW locking tab put in and bent towards the bolts, to lock them in place)

Nope, not the wrist pin off the piston.

On this motor, there's a counterweight that the crank spins in... made of cast Iron/ There is a link that this counterweight articulates on between 2 pins. One pin is located between the 2 halves of the counterweight, & the other pin is press-fit into the crank case. (right below the camshaft) The link that goes between the two pins keeps the counter-weight from hitting the inside wall of the crank case. This connecting link is made from cast aluminum.

I guess this may be the "syncro-balance" end of the motor.
I'm hoping to just find another running motor instead of fooling with this one any more. Although, I may have my own solution if I can get a couple of machined parts made.

Score! I picked up a whole mower with a 12.5 with a bad starter for $80.
It's a bit older than mine. I'm going to transfer the carb & starter & muffler.
Hopefully this will suffice for a while. The way my luck has been, I'll end up having to just go out & spend the $$ & buy a new mower! Thanks briggsdude for your input.

No problem...

As for the engine, you may end up swapping the wiring too!! so don't go cutting it up...
And measure the pulley on the new (well used) engine and the old one.. make sure they match up, close enough will do though.

Your crankshaft bearing is spun pull it out of your motor and check to see if you have lines or groves in your crank if you do there is no fixingit just that you will need a new crank